1. Field of the Invention
The present invention relates to an automatic-tracking camera apparatus which is provided with a camera capable of continuously acquiring images and which automatically tracks a target object, such as a person.
2. Description of the Related Art
There has been conventionally known a camera with a pan/tilt rotation mechanism intended for remote control or automatic control in the shooting direction. Meanwhile, there has also been known a technique for detecting the position, the movement speed and the like of a particular target object, such as a person using a technique, such as image recognition, ultrasonic detection, detection by a temperature sensor, or the like. By detecting the position or the movement speed of a predetermined target object with the use of the latter technique and controlling the rotation of the former camera on the basis of the detected values, a tracking operation for automatically catching the target object within the image-taking range of the camera can be performed. Especially, by detecting the target object by the recognition technique with the use of the camera of a pun/tilt camera as a detection device, tracking can be performed with a compact device economically, without necessity of separately preparing a new sensor. Further, it is characterized that, since detection and shooting direction control are performed with the same camera, the configuration is simpler in comparison with an apparatus provided with a sensor and a rotary camera separately.
This kind of automatic-tracking camera apparatus is used, for example, in systems for monitoring of a suspicious person, tracking of a target object in a factory, control of the angle of view in TV relay broadcasting of sports, and the like. As the control method of the automatic-tracking camera, it is usual to detect the position of a target object in an image, specify the angle of driving a rotary camera, and control the rotation by specifying the number of pulses of a servo-controller or a stepping motor on the camera side. As another method, there is a method in which, when a target object is detected, the speed of a rotary camera is controlled so that the movement (motion blur) of the image within the target area is made as little as possible (for example, see Japanese Laid-Open Patent Publication (Kokai) No. 05-30406). A method is also known in which variation between a target object in an image and a target position is detected, and appropriate gain is applied to directly control the actuator of a rotary camera (vision feedback control) (for example, see Japanese Laid-Open Patent Publication (Kokai) No. 2002-189519).
However, in the target detection methods using an image, image acquisition itself requires a lot of time. In a common video camera, the image acquisition rate is 30 frames per second. Further, commonly, the subsequent target detection processing also requires time equal to the time required for image acquisition or more.
The rotation driving control of a rotary camera is generally performed with the use of a sensor attached to the rotation mechanism on the camera side (except for the case of the vision feedback control and the like). For example, the rotation driving control is performed with the use of an angle sensor such as a rotary encoder, an acceleration or speed sensor such as a gyro-sensor, or the current sensor of a motor. In addition, a method of controlling the number of driving pulses with the use of a stepping motor is also used. The speed of these methods is generally faster than that in the case of sensing using an image, and it is capable of realizing dozens to thousands of times faster sampling rate.
FIG. 35 is a block diagram showing rotation driving control in a conventional automatic-tracking camera apparatus. In this apparatus, variation between the position of a target object and a target position is determined from an image detection result; target coordinates of the camera are set on the basis of the determined value, and a high-speed sensor on the camera side is used to perform control to reach the values, as shown in FIG. 35. In comparison with the time required for steps S101 to S107 in FIG. 35, steps S109 to S111, which are steps for control of the rotation of the camera, are performed at a higher speed due to the control operation step S110 and the like.
FIG. 36 is a diagram showing the time response of the camera position in the case where driving is performed in the configuration shown in FIG. 35. FIG. 37 is a diagram showing the time response of the camera speed in the case where driving is performed in the configuration shown in FIG. 35. In such a configuration, since control is performed on the basis of the position, position variation (deviation) due to accumulation does not occur if the control system is appropriately configured. However, there is a problem that, since abrupt acceleration and abrupt deceleration are performed before the target position is reached, the movement is not smooth.
That is, there is a risk that, because of repetition of stop-go (stop and start of driving), vibrations synchronized with the cycle or a strange sound may occur. This vibrations may cause image blurring and the like, thereby affecting the quality of an acquired image. As shown in FIG. 37, in a different design, it is possible to acquire an image during a stable time period when the position varies little. However, since the speed is “0” during the period, the probability that the difference from the speed of a tracking target is much is high.
Therefore, as shown in FIG. 38, the acquired image is such that the tracking target object is blurred though the background is not blurred. The next target position is determined on the basis of this image. Therefore, if the blurring worsens, it causes problems that the target object cannot be extracted or that the position accuracy decreases. As a result, in the case of a tracing target moving at a high speed, it is difficult to accurately track it.
Meanwhile, there is also a method in which speed is specified as the each-time controlled quality. For example, as shown in FIG. 39, there is a double-loop control method in which speed control is performed by an inner loop and position control is performed by an outer loop. Here, the output of the transfer function of a rotation mechanism 103 is speed. An integrator (1/s) 104 is also provided. FIGS. 40 and 41 show a time response and a speed response of the camera position in this method, respectively.
In this case, since driving is continuous, there is not a risk that generation of vibrations and a strange sound due to abrupt acceleration, abrupt deceleration, or stop-go may occur, unlike the case of the position specification. Further, since control is performed at a predicted speed of a target object during image acquisition time, it is characterized that the blurring of the target object is little though the background is blurred, as shown in FIG. 42. As a result, even if the tracking target moves at a high speed, the image blurring of the target object is little. Therefore, the quality of the image corresponding to the part to be tracked, within the image used for recognition, does not deteriorate, and therefore, the detection probability and accuracy do not decrease.
However, it is not assured that a speed profile corresponds to the movement of a tracking target. If they do not correspond to each other, position variation occurs. If the position variation is accumulated, there is a risk that the target object is missed in the worst case. Further, there may be an abrupt acceleration part though it is not so serious as in the position-specification control method. Therefore, there is a problem that driving is not sufficiently smooth.
Furthermore, since high-level response is required from the inner-loop speed control, high gain is required. Therefore, if delay occurs because of slow response of the rotation mechanism as an object to be controlled, or if cogging of a motor or nonuniform load by a transfer system such as a gear occurs, oscillation easily occurs, and the control system tends to be unstable. Therefore, this method cannot be necessarily applied to all objects to be controlled.